Opposition Leader Tony Abbott has poured scorn on Labor's new plan to move to an emissions trading scheme one year early, describing an ETS as ''not a true market''.

''Just ask yourself what an emissions trading scheme is all about. It's a so-called market in the non-delivery of an invisible substance to no one,'' he said, when addressing reporters in Camden, in south-west Sydney, on Monday.

Mr Abbott's comments come as the federal government defends its plan to end the carbon tax one year early.

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This would see Australia move from the present fixed carbon price of $24.15 a tonne to the floating European price, at present about $6 a tonne, on July 1, 2014.

Treasurer Chris Bowen conceded on Monday that while the move would ease cost of living pressures, it would see a ''significant'' hit to the federal budget, in the billions of dollars.

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But he would not be drawn on how much the carbon tax decision would cost the budget or what the government would do to pay for it - saying this would be announced in coming days. Mr Bowen also would not say whether or not Parliament would be recalled to legislate the changes before the federal election. He said the timing was up to the Prime Minister.

''One way or another'' - either through the Parliament or an election - Labor would seek a mandate to make the change, he told Fairfax Radio.

''What we had from Tony Abbott today was another example of why he's simply not up to the task of being Australia's prime minister,'' Senator Wong said.

''A man who thinks that climate change is, in his words, 'absolute crap', now mocking the very design that John Howard himself put forward to deal with climate change.''

Mr Abbott's stance on the regulation of carbon emmissions appears to be at odds with that of shadow communications minister Malcolm Turnbull, who lost his position as Liberal leader in 2009 due to his support for an ETS.

Last week, Mr Turnbull told ABC's Q&A program that he hoped the world moved towards a market-based scheme.